Electroluminescent display device

ABSTRACT

The invention is directed to an electroluminescent display device in which a first planarization insulating film need not be used so that a manufacturing cost reduces, and a display defect caused by a cut in an organic EL layer or moisture absorption at a step portion is prevented. An R color filter layer, a G color filter layer, and a B color filter layer are so formed that end portions of the adjacent R, G, and B color filter layers overlap each other. The R color filter layer, the G color filter layer, and the B color filter layer serve as a first planarization insulating film. For planarization, the end portions of the color filter layers overlap each other. For reducing a step height of an overlapping portion, the end portions of the color filters are formed in a tapered shape.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The invention relates to an electroluminescent display device,particularly to an electroluminescent display device having color filterlayers.

[0003] 2. Description of the Related Art

[0004] An organic electroluminescent (hereafter, referred to as EL)element is a self-emission element. An organic EL display device usingthe organic EL element is receiving an attention as a new display devicesubstituted for a CRT or an LCD.

[0005]FIG. 5 is a schematic cross-sectional view showing a pixel of afull-color organic EL display device of the conventional art. A numeral200 designates a glass substrate, a numeral 201 designates an organic ELelement driving TFT (thin film transistor) formed on the glass substrate200, and a numeral 202 designates a first planarization insulating film.A numeral 203 designates an anode layer made of ITO (indium tin oxide)which is connected with the TFT 201 and extends over the firstplanarization insulating film 202, and a numeral 204 designates a secondplanarization insulating film formed so as to cover an end portion ofthe anode layer 203. A numeral 205 designates R (red), G (green), and B(blue) organic EL layers formed on the anode layer 203, and a numeral206 designates a cathode layer formed on the organic EL layer 205.

[0006] A glass substrate 207 covers the cathode layer 206. The glasssubstrate 207 and the glass substrate 200 are attached at their edges,and the R, G, and B organic EL layers 205 are enclosed therein. Here,the R, G, and B organic EL layers 205 are respectively formed byselectively performing vapor-deposition of each of R, G, and B organicEL materials by using a metal mask.

[0007] On the other hand, as a method of realizing a full-color organicEL display device without using the above R, G, and B organic EL layers205, a method of using color filter layers has been proposed. In thiscase, a combination of a white organic EL layer and color filter layersis employed.

[0008]FIG. 6 is a cross-sectional view of such a full-color organic ELdisplay device. An insulating layer 301 as a substrate is formed on theglass substrate 300, and an R color filter layer 302, a G color filterlayer 303, and a B color filter layer 304 are formed on the insulatingfilm 301. Each of these color filter layers transmit light having apredetermined wavelength corresponding to each of the R, G, and Bcolors, which is irradiated from the white organic EL layer. Althoughnot shown, an organic EL element driving TFT is formed under these colorfilter layers 302, 303, and 304 in a manner similar to the TFT 201 ofFIG. 5.

[0009] A first planarization insulating film 305 is formed on thesecolor filter layers 302, 303, and 304. Anode layers 306, 307, and 308are formed on the first planarization insulating film 305, correspondingto each of the R, G, and B colors. A second planarization insulatingfilm 309 is formed so as to cover end portions of the anode layers 306,307, and 308, and a white organic EL layer 310 and a cathode layer 311are laminated thereon in this order. Furthermore, a glass substrate 312covers the cathode layer 311, and the glass substrate 312 and the glasssubstrate 300 are attached at their edges, so that the white organic ELlayer 310 is enclosed therein.

[0010] Here, the reason to provide the second planarization insulatingfilm 309 is that the distance between the anode layers 306, 307, and 308and the cathode layer 311 becomes small without the second planarizationinsulating film 309 and may cause a short circuit. The secondplanarization insulating film 309 is formed with openings except abovethe end portions of the anode layers 306, 307, and 308, and the whiteorganic EL layer 310 is in contact with the anode layers 306, 307, and308 exposed in the openings.

[0011] The organic EL display device of this type is described in aJapanese Patent Application Publication No. Hei 11-251059.

[0012] However, the organic EL display device employing the describedstructure of the white organic EL layer and the color filter layers hasfollowing problems. Firstly, since the first planarization insulatingfilm 305 is formed on the R color filter layer 302, the G color filterlayer 303, and the B color filter layer 304, a manufacturing costincreases accordingly. This can be solved by eliminating the firstplanarization insulating film 305 by using the color filter layers asthe first planarization insulating film 305. In this case, the adjacentcolor filter layers need to overlap each other for planarization and forincreasing an aperture ratio. However, since the step height at theoverlapping portion of the color filter layers becomes large, a displaydefect may occur by a cut in the organic EL layer, moisture absorptionat the step portion, and so on.

[0013] Secondly, as the first planarization insulating film 305, organicresin such as acrylic resin having a thickness of 2 to 3 micrometersmust be used for planarization. However, since the organic resin hashigh moisture absorbency, it can have an adverse effect on the organicEL layer which is sensitive to moisture, causing a display defect.

SUMMARY OF THE INVENTION

[0014] The invention provides a color electroluminescent display devicethat includes a plurality of color pixels and a plurality of colorfilter layers provided for the color pixels on an insulating substrate.Each of the color filter layers allows a transmission of light of acolor of a corresponding color pixel. The display device also includesan anode layer formed on each of the color filter layers, a whiteelectroluminescent layer formed on the anode layers, and a cathode layerformed on the white electroluminescent layer. End portions of the colorfilter layers are tapered, and the tapered end portions of adjacentcolor filter layers overlap each other. A thin planarization insulatingfilm may be formed directly on the color filter layers in addition toanother planarization insulating film that covers end portions of theanode layers.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015]FIG. 1 is a cross-sectional view of an organic EL display deviceof an embodiment of the invention.

[0016]FIGS. 2A, 2B, 2C, and 2D are cross-sectional views of processingsteps of color filter layers of the display device of FIG. 1.

[0017]FIG. 3 is a cross-sectional view of a modified organic EL displaydevice of the embodiment of the invention.

[0018]FIG. 4 is an equivalent circuit diagram of the organic EL displaydevice of the embodiment of the invention.

[0019]FIG. 5 is a cross-sectional view of a conventional organic ELdisplay device.

[0020]FIG. 6 is a cross-sectional view of another conventional organicEL display device.

DETAILED DESCRIPTION OF THE INVENTION

[0021] An embodiment of the invention will be described with referenceto the drawings. FIG. 1 is a cross-sectional view showing a pixel of anorganic EL display device of the embodiment of the invention. In anactual organic EL display device, a plurality of the pixels is arrangedin a matrix.

[0022] An insulating film 2 made of SiO₂ as a substrate is formed on aglass substrate 1. An R color filter layer 3, a G color filter layer 4,and a B color filter layer 5 are formed adjacent each other on theinsulating film 2. Each of these color filter layers transmits lighthaving a predetermined wavelength corresponding to each of R, G, and Bcolors, which is irradiated from a white organic EL layer 10. Althoughnot shown, an organic EL element driving TFT and a pixel selecting TFTare formed under these color filter layers.

[0023] The R color filter layer 3, the G color filter layer 4, and the Bcolor filter layer 5 also serve as a first planarization insulatingfilm, such as the one 202 in FIG. 5. End portions of the color filterlayers are overlapped for planarization. The end portions of the colorfilter layers are formed in a tapered shape so as to reduce a stepheight H2 at an overlapping portion. For example, the both end portionsof the R color filter layer 3 are formed in a tapered shape, and one ofthe end portions of the G color filter layer 4 is formed to cover one ofthe end portions of the R color filter layer 3. Furthermore, the bothend portions of the B color filter layer 5 are formed to respectivelycover the end portion of the R color filer layer 3 and the end portionof the G color filter layer 4.

[0024] A conventional planarization insulating film is not formed onthese color filter layers, but anode layers 6, 7, and 8 are formeddirectly on the R color filter layer 3, the G color filter layer 4, andthe B color filter layer 5, respectively. Furthermore, a secondplanarization insulating film 9 is formed to cover end portions of theanode layers 6, 7, and 8, and a white organic EL layer 10 and a cathodelayer 11 are laminated thereon in this order. A glass substrate 30covers the cathode layer 11, and the glass substrate 30 and the glasssubstrate 1 are attached at their edges to enclose the white organic ELlayer 10 therein.

[0025] The reason to provide the second planarization insulating film 9is the same as the conventional art, that is, the distance between theanode layers 6, 7, and 8 and the cathode layer 11 becomes small withoutthe second planarization insulating film 9 so that a short circuit canoccur between the anode layers 6, 7, and 8 and the cathode layer 11.Openings are formed in the second planarization insulating film 9 exceptabove the end portions of the anode layers 6, 7, and 8. The whiteorganic EL layer 10 is formed on the anode layers 6, 7, and 8 exposed inthe openings, being in contact therewith.

[0026] A forming method of the color filter layers will be describedwith reference to FIGS. 2A, 2B, 2C, and 2D. Here, a forming method ofthe R color filter layer 3 and the G color filter layer 4 will bedescribed. As shown in FIG. 2A, the R color filter material layer 3 amade of a negative photoresist containing a predetermined pigment iscoated on the whole surface of the insulating film 2 serving as asubstrate formed on the glass substrate 1. Then, the R color filtermaterial layer 3 a is exposed to light through predetermined masks 12.When the R color filter material layer 3 a undergoes next developmenttreatment, as shown in FIG. 2B, a portion of the R color filter materiallayer 3 a which is exposed to light remains to form the R color filterlayer 3. The R color filter layer 3 is formed by this exposure anddevelopment process, having tapered portions at its ends. This isbecause that the R color filter material layer 3 a receives light beyondthe area corresponding to the opening of the mask 12 with an intensitythat is smaller than that of the central portion of the mask and isgradually decreasing.

[0027] Next, as shown in FIG. 2C, a G color filter material layer 4 amade of a negative photoresist containing a predetermined pigment iscoated on the whole surface. The G color filter material layer 4 a isexposed to light through predetermined masks 13. When the G color filtermaterial layer 4 a undergoes next development treatment, as shown inFIG. 2D, a portion of the G color filter material layer 4 a which isexposed to light remains to form the G color filter layer 4. Bypositioning the masks 13 as shown in FIG. 2D, the end portion of the Gcolor filter layer 4 overlaps the end portion of the R color filterlayer 3.

[0028] The end portion of the R color filter layer 3 is formed in atapered shape. The end portion of the G color filter layer 4 has atapered shape and becomes gradually thinner toward its end. Therefore, astep height H2 of an overlapping portion of the G color filter layer 4and the R color filter layer 3 is reduced. The forming method of the Bcolor filter layer 5 is the same as this.

[0029] Here, the less the step height H2 of the overlapping portion ofthe R, G, and B color filter layers is, the better the display performs.However, for preventing a cut in the white organic EL layer 9 formedabove the R, G, and B color filter layers, which can be caused by thestep height H2, when a film thickness of the white organic EL layer 9 isH1, it is preferable that H1 is larger than H2. In this embodiment, bothend portions of the B color filter layer 5 are formed to cover the endportions of the adjacent R color filter layer 3 and G color filter layer4, respectively.

[0030] For minimizing the step height H2 of the overlapping portion ofthe color filter layers, the color filter layers are preferably formedin a decreasing order of thickness. For example, when the thicknesses ofthe R color filter layer 3, the G color filter layer 4, and the B colorfilter layer 5 are T1, T2, and T3, respectively, it is preferable thatT1 is lager than T2 and T2 is larger than T3. In this case, the R colorfilter layer 3, the G color filter layer 4, and the B color filter layer5 are formed in this order.

[0031] Accordingly, in this embodiment, the R color filter layer 3, theG color filter layer 4, and the B color filter layer 5 serve as thefirst planarization insulating film. However, as shown in FIG. 3, thefirst planarization insulating film 20 can be further formed on thesecolor filter layers. This first planarization insulating film 20 can beformed thinner than the conventional art since the planarization isalready realized to some extent by the R color filter layer 3, the Gcolor filter layer 4, and the B color filter layer 5. A preferable filmthickness is between 200 nm and 300 nm.

[0032] Furthermore, since the first planarization insulating film 20 isthin, the first planarization insulating film 20 can be formed of aninorganic insulating film having low absorbency by a PCVD(plasma-activated chemical vapor deposition) method. It is preferable toemploy a silicon oxide film, a TEOS film, or a silicon nitride film asthe inorganic insulating film.

[0033] Next, an equivalent circuit of the described organic EL displaydevice and its operation will be described. FIG. 4 is an equivalentcircuit diagram of the organic EL display device, showing a pixel formedin a periphery of a gate signal line 50 at an n-th row and a drainsignal line 60 at an m-th column.

[0034] The gate signal line 50 for supplying a gate signal Gn and thedrain signal line 60 for supplying a drain signal, that is, a videosignal Dm cross each other. An organic EL element 120, a TFT 100 fordriving the organic EL element 120, and a TFT 110 for selecting a pixelare formed in a periphery of an intersection of the both signal lines 50and 60.

[0035] A drive source 105 is connected with a drain 100d of the organicEL element driving TFT 100, and supplies a positive drive voltage PVdd.A source 100 s is connected with an anode 121 of the organic EL element120.

[0036] A gate 110 g of the selecting TFT 110 for selecting a pixel isconnected with the gate signal line 50 and supplied with a gate signalGn. A drain 110 d is connected with the drain signal line 60 andsupplied with the video signal Dm. The source 110 s of the selecting TFT110 is connected with the gate 100 g of the driving TFT 100. Here, thegate signal Gn is outputted from a gate driver circuit (not shown). Thevideo signal Dm is outputted from a drain driver circuit (not shown).

[0037] The organic EL element is made of the anode 121, a cathode 122,and an emissive layer 123 formed between the anode 121 and the cathode122. The cathode 122 is connected with a common source 140 for supplyinga negative common voltage CV.

[0038] Furthermore, the gate 100 g of the driving TFT 100 is connectedwith a storage capacitor 130. That is, one electrode of the storagecapacitor 130 is connected with the gate 100 g, and another electrodethereof is connected with the storage capacitor electrode 131. Thestorage capacitor 130 is provided for storing the video signal of thepixel for one field period by storing electric charge corresponding tothe video signal Dm.

[0039] An operation of the EL display device having the describedstructure will be described as follows. When the gate signal Gn becomeshigh level for one horizontal period, the selecting TFT 110 turns on.Then, the video signal Dm is applied from the drain signal line 60 tothe gate 100 g of the driving TFT 100 through the selecting TFT 110. Inresponse to the video signal Dm supplied to the gate 100 g, conductanceof the driving TFT 100 changes. The drive electric current correspondingto the conductance is supplied from the drive source 105 to the organicEL element 120 through the driving TFT 100. Accordingly, luminance ofthe organic EL element 120 is controlled.

[0040] Although colors of the color pixels and the color filter layersare R (red), G (green), and B (blue) in this embodiment, the colors maybe yellow or magenta. Furthermore, the “white EL” is mainly white, butmay be reddish or bluish.

What is claimed is:
 1. A color electroluminescent display devicecomprising: a plurality of color pixels; a plurality of color filterlayers provided for the color pixels on an insulating substrate, each ofthe color filter layers allowing a transmission of light of a color of acorresponding color pixel; an anode layer formed above each of the colorfilter layers; a white electroluminescent layer formed on the anodelayers; and a cathode layer formed on the white electroluminescentlayer, wherein end portions of the color filter layers are tapered, andthe tapered end portions of adjacent color filter layers overlap eachother.
 2. The color electroluminescent display device of claim 1,wherein a step height at an overlapping portion of the color filterlayers is smaller than a thickness of the white electroluminescentlayer.
 3. The color electroluminescent display device of claim 1,wherein the color filter layers have different thicknesses and endportions of thinner color filter layers are disposed above end portionsof thicker color filter layers.
 4. A color electroluminescent displaydevice having a plurality of color pixels, comprising: a plurality ofcolor filter layers provided for the color pixels on an insulatingsubstrate, each of the color filter layers allowing a transmission oflight of a color of a corresponding color pixel; a planarizationinsulating film formed on the color filter layers; anode layers formedon the planarization insulating film; a white electroluminescent layerformed on the anode layers; and a cathode layer formed on the whiteelectroluminescent layer, wherein end portions of the color filterlayers are tapered, and the tapered end portions of adjacent colorfilter layers overlap each other.
 5. The color electroluminescentdisplay device of claim 4, wherein a step height at an overlappingportion of the color filter layers is smaller than a thickness of thewhite electroluminescent layer.
 6. The color electroluminescent displaydevice of claim 4, wherein the color filter layers have differentthicknesses and end portions of thinner color filter layers are disposedabove end portions of thicker color filter layers.
 7. The colorelectroluminescent display device of claim 4, wherein the planarizationinsulating film comprises an inorganic insulating film.
 8. The colorelectroluminescent display device of claim 7, wherein the inorganicinsulating film is a silicon oxide film, a TEOS film or a siliconnitride film.
 9. A color electroluminescent display device having aplurality of color pixels, comprising: a plurality of color filterlayers provided for the color pixels on an insulating substrate, each ofthe color filter layers allowing a transmission of light of a color of acorresponding color pixel; a first planarization insulating film formedon the color filter layers; anode layers formed on the firstplanarization insulating film; a second planarization insulating filmformed so as to cover end portions of the anode layers; a whiteelectroluminescent layer formed on the anode layers; and a cathode layerformed on the white electroluminescent layer; wherein end portions ofthe color filter layers are tapered, and the tapered end portions ofadjacent color filter layers overlap each other.
 10. The colorelectroluminescent display device of claim 9, wherein a step height atan overlapping portion of the color filter layers is smaller than athickness of the white electroluminescent layer.
 11. The colorelectroluminescent display device of claim 9, wherein the color filterlayers have different thicknesses and end portions of thinner colorfilter layers are disposed above end portions of thicker color filterlayers.
 12. The color electroluminescent display device of claim 9,wherein the first planarization insulating film comprises an inorganicinsulating film.
 13. The color electroluminescent display device ofclaim 12, wherein the inorganic insulating film is a silicon oxide film,a TEOS film or a silicon nitride film.
 14. A color electroluminescentdisplay device comprising: a first pixel of a first color; a scone pixelof a second color disposed adjacent the first pixel; a first colorfilter layer provided for the first pixel and allowing a transmission oflight of the first color, the first color filter layer having a taperedend portion; a second color filter layer provided for the second pixeland allowing a transmission of light of the second color, the secondcolor filter layer having a tapered end portion; a first anode layerformed on the first color filter layer; a second anode layer formed onthe second color filter layer; a white electroluminescent layer formedon the first and second anode layers; and a cathode layer formed on thewhite electroluminescent layer, wherein the tapered end portion of thefirst color filter layer is disposed over the tapered end portion of thesecond color filter layer.
 15. The color electroluminescent displaydevice of claim 14, wherein a thickness of the first color filter layeris smaller than a thickness of the second color filter layer.